The present invention relates to a composite-type magnetic head which is built up of a soft magnetic metal film and a magnetic or non-magnetic substrate supporting it.
The recent introduction of high-coercivity tapes have necessitated the development of magnetic heads which employ a soft magnetic metal film having a high saturation magnetic flux density. These magnetic heads are constructed such that a soft magnetic metal film is held between high wear-resistance magnetic or non-magnetic substrates, so that they are subject to less wear by sliding travel and have a longer wear life.
A composite-type magnetic head suffers so-called level difference (due to the unbalanced wear that occurs at the boundary between different materials) unless the materials constituting the head sliding surface have the same wear characteristics. The level difference leads to an increased spacing loss at the time of recording and playback.
A conventional countermeasure to cope with the level difference is to constitute the head sliding surface with materials having the same wear characteristics. An example of this countermeasure is disclosed in Japanese Patent Laid-open No. 1-102713. According to this disclosure, a proper amount of Bi.sub.2 O.sub.3 is added to the major component (.alpha.-Fe.sub.2 O.sub.3) for the substrate (thereby to lower its wear resistance) so that the substrate has the same wear characteristics as the soft magnetic metal film made of amorphous alloy or sendust (Fe-Al-Si alloy) to thereby obtain a magnetic head having a small level difference namely a low spacing loss.
Although the addition of Bi.sub.2 O.sub.3 reduces the level difference, it also increases the wear rate of the substrate and hence aggravates the wear resistance of the head as a whole. For the magnetic head to have a desired life in this situation, it is necessary to increase the gap depth excessively. However, the increased gap depth lowers the magnetic circuit efficiency and hence offsets the effect of reducing the spacing loss due to the level difference. Incidentally, the magnetic circuit efficiency is defined by the ratio of the magnetic flux of tapes which passes through the head coil when the magnetic head is represented by an equivalent magnetic circuit with magnetic reluctance.
There is another approach to the elimination of level difference. In this case, the substrate is made of a wear-resistant material and the soft magnetic metal film is made to have a high wear resistance comparable to that of the substrate. It is reported that it is possible to improve the wear characteristics of the soft magnetic metal film by the incorporation of nitrogen. However, the improvement by this means is not satisfactory for practical use. In fact, the wear rate of the soft magnetic metal film is still nearly ten times that of the substrate.